Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $25.52   5.510%   $26.9262   $26.93   $26.95   $26.90  
  Purchase #2 $208.32   7.828%   $224.6273   $224.63   $224.65   $224.60  
  Purchase #3 $231.88   4.554%   $242.4398   $242.44   $242.45   $242.40  
  Purchase #4 $214.83   11.635%   $239.8255   $239.83   $239.85   $239.80  
  Purchase #5 $13.71   6.793%   $14.6413   $14.64   $14.65   $14.60  
  Purchase #6 $31.52   6.125%   $33.4506   $33.45   $33.45   $33.50  
  Purchase #7 $200.76   12.710%   $226.2766   $226.28   $226.30   $226.30  
  7 purchase totals = $926.54       $1,008.1873   $1,008.20   $1,008.30   $1,008.10